1. Field of Invention
The invention relates to a piezoelectric actuator and a fluid jet apparatus including the piezoelectric actuator and a manufacturing method for the piezoelectric actuator and the fluid jet apparatus.
2. Description of Related Art
A known fluid jet apparatus, for example, an ink-jet print head that ejects a droplet of fluid, such as ink, includes a piezoelectric element. Such ink-jet print head uses a plate member made of a piezoelectric material for a wall of a chamber that contains ink therein. Upon the application of a voltage to the piezoelectric material, the wall is deformed so as to apply pressure to the ink in the chamber. Therefore, the ink is ejected from a nozzle connected to the chamber.
The piezoelectric material is generally deformed in a shear mode or direct mode. In a direct mode, as a drive voltage is applied, a drive electric field is generated in the piezoelectric material in a direction parallel to a polarization direction of the piezoelectric material. The piezoelectric material deforms in direct mode in a direction parallel to the polarization direction of the piezoelectric material. In a shear mode, as a drive voltage is applied, a drive electric field is generated in the piezoelectric material in a direction substantially perpendicular to a polarization direction of the piezoelectric material. The piezoelectric material deforms in a direction of the shearing of the piezoelectric material.
A shear mode type ink-jet print head is disclosed in, for example, U.S. Pat. No. 5,266,964. The ink-jet print head disclosed in U.S. Pat. No. 5,266,964 includes internal electrodes used as electrodes for polarization, and external electrodes used as drive electrodes.
An ink-jet print head disclosed in U.S. Pat. No. 5,128,694 has slits formed in portions of a piezoelectric element which faces ink chambers. An area defined by the slits forms a first pressure portion, and a set of first electrodes is disposed in the first pressure portion. An area defined by the other slits forms a second pressure portion, and a set of second electrodes is disposed in the second pressure portion.
One aspect of the invention is to provide an improved piezoelectric actuator including internal electrodes and to provide a fluid jet apparatus including such a piezoelectric actuator.
Another aspect of the invention is to provide a method for manufacturing an improved piezoelectric actuator including internal electrodes and a fluid jet apparatus including such a piezoelectric actuator.
According to one aspect of the invention, a piezoelectric actuator may include a piezoelectric plate that is made of at least one sheet of piezoelectric material, a set of a plurality of first internal electrodes that are provided in one direction in the piezoelectric plate with a space therebetween, a set of a plurality of second internal electrodes that are provided in the one direction in the piezoelectric plate so as to correspond to the first internal electrodes with a space between the first internal electrodes and the second internal electrodes, and a groove that is formed in the one direction in the piezoelectric plate so as to expose ends of at least one of the set of the first internal electrodes and the set of the second internal electrodes. The piezoelectric material between the first internal electrodes and the second internal electrodes is polarized.
According to another aspect of the invention, a method for manufacturing a piezoelectric actuator may include the steps of forming in a piezoelectric plate that is made of at least one sheet of piezoelectric material, a first internal electrode pattern including a set of a plurality of first internal electrodes disposed in one direction with a space therebetween and a first lead that interconnects the first internal electrodes, and a second internal electrode pattern including a set of a plurality of second internal electrodes disposed in the one direction so as to correspond to the first internal electrodes with a space between the first internal electrodes and the second internal electrodes and a second lead that interconnects the second internal electrodes, polarizing the piezoelectric material between the first internal electrodes and the second internal electrodes in the one direction by applying an electric field between the first internal electrodes and the second internal electrodes through the first lead and the second lead, and separating at least one of the set of the first internal electrodes and the set of the second internal electrodes individually after the polarizing step, by removing at least one of the first lead and the second lead.